Scary thing, darkness (5)
I believe the answer is:
night
'darkness' is the definition.
(night is a kind of darkness)
'scary thing' is the wordplay.
'scary' indicates an anagram (I've seen this in other clues).
'thing' anagrammed gives 'NIGHT'.
(Other definitions for night that I've seen before include "Saturday -- Fever (film)" , "Tennyson's "black bat"" , "'The 2 8 of the dog in the _____'" , "Dark hours" , "Time between days" .)